Different types of monochromators and polychromators are described in a book by J. Sternberg "The Design of Optical Spectrometers", Chapman and Hall, 1969, and in a book by Y. Talmi "Multichannel Image Detectors", American Chemical Society, 1979.
U.S. Pat. No. 4,820,048 describes an Echelle polychromator combined with a novel solid-state detector array. A separation of the orders within the Echelle polychromator is performed for a simultaneous detection of the complete wavelength range. This results in a limitation in the entrance slit height. Furthermore, imaging errors arise at the end portions of the spectrum. The level of scattered light is relatively high.
GB-A-2 204 964 describes an Echelle polychromator for multiple element analysis. A light source produces a light bundle defined by two crossed entrance slits. The light bundle impinges onto a collimator mirror. The collimator mirror directs the light bundle directed in parallel through a dispersion prism onto an Echelle grating. The light bundles diffracted by the Echelle grating repass through the dispersion prism and are collected by a camera mirror onto a two-dimensional detector array. The dispersion prism effects dispersion in a direction vertical to the direction of dispersion of the Echelle grating, and thus a separation of the different orders of the Echelle grating. The detector array comprises detector elements at the locations of characteristic spectrum lines of the various chemical elements to be determined.
An Echelle monochromator is known in which the orders are separated by a pre-monochromator. The pre-monochromator produces a spectrum on the plane of an entrance slit of the high-resolution Echelle monochromator. Only a limited wavelength range of that spectrum enters into the Echelle monochromator. Then, the Echelle monochromator takes from this wavelength range a more narrow wavelength range by means of an exit slit and a detector positioned downstream thereof. Such dual Echelle monochromators achieve a high spectral resolution at an extremely small amount of stray light. A high light guide number results from the larger height of the slits. However, only one spectral position within the total spectrum can be investigated at a time (P. W. J. M. Boumans and J. J. A. M. Vrakking, "Spectrochimica Acta" Bd. 39B No. 9-11, 1239).
DE-C-3 634 485 describes a liquid prism having a variable prism angle for producing spectrally distorted photographs and projections.